Triggered Lightning: Implement Layer Mean Temperature Plugins by Anzerkhan27 · Pull Request #2321 · metoppv/improver

Anzerkhan27 · 2026-03-03T15:10:30Z

This PR implements the mean layer temperature calculation step as part of the ongoing migration of the Helicopter-Triggered Lightning (GPP → EPP) workflow (eppuk_triggered_lightning).

The GPP implementation contained a single monolithic function calculate_layer_mean_temperature() which handled both the vertical layer extraction and the weighted mean calculation in one function. This PR introduces two IMPROVER-style plugins to replace this, following EPP conventions.

Two new plugins have been implemented:

1. `LayerExtractionAndInterpolation`

Extracts all UKV temperature model levels falling strictly between 2000 ft and 3000 ft (converted to metres).
Interpolates temperature at the exact 2000 ft and 3000 ft boundaries using iris.analysis.Linear().
Concatenates the interpolated boundaries with the extracted interior levels into a single cube.

2. `CalculateLayerMeanTemperature`

Takes the output of LayerExtractionAndInterpolation as input.
Computes the altitude-weighted mean temperature across the layer using a trapezoidal weighting scheme (thickness between levels as weights).
Returns a 2D Iris cube (projection_y_coordinate, projection_x_coordinate) with scalar coordinates forecast_period, forecast_reference_time, and time preserved from the input.
Output metadata uses standard_name="air_temperature" (CF convention) with units="K".

…-lightning-layer-mean-temperature-plugin

robertplatt-mo

@Anzerkhan27 I've requested a few changes the main comments being in layer_mean_temperature and probably the most time consuming being type hints which I understand improver style guide expects.

Generally it all looks pretty sensible though.

robertplatt-mo · 2026-03-06T13:06:20Z

improver/temperature/layer_mean_temperature.py

+        Initialise the plugin.
+
+        Args:
+            metres_to_ft (float): Conversion factor from metres to feet.


This feels like a curious thing to have as an argument. Surely the conversion value for metres in to ft is always the same? Why would we want to make it available to users?

I agree with you. The conversion value will always remain the same and its no point of adding it as argument. I have moved it to the top of the file as a constant

robertplatt-mo · 2026-03-06T13:17:37Z

improver/temperature/layer_mean_temperature.py

+            raise ValueError(f"bottom ({bottom} ft) must be less than top ({top} ft).")
+
+        if verbosity:
+            print(f"Extracting/interpolating levels from {bottom} to {top} ft")


I'm not particularly keen on this catch all tbh. I'd suggest either remove Extracting/ so this comment better reflects that the main role of the function is to interpolate the levels (given my comments elsewhere that say that extracting is just in service of the temperature interpolation), or keep extraction here and add additional verbose entries for extracting base temp and extracting top temp.

robertplatt-mo · 2026-03-06T13:18:07Z

improver/temperature/layer_mean_temperature.py

+                            (base, interior, and top).
+        """
+        if bottom >= top:
+            raise ValueError(f"bottom ({bottom} ft) must be less than top ({top} ft).")


Suggested change

raise ValueError(f"bottom ({bottom} ft) must be less than top ({top} ft).")

raise ValueError(f"Bottom ({bottom} ft) must be less than top ({top} ft).")

robertplatt-mo · 2026-03-06T13:20:09Z

improver/temperature/layer_mean_temperature.py

+from improver import BasePlugin
+
+
+class LayerExtractionAndInterpolation(BasePlugin):


I'm not keen on the name of this plugin. Firstly extract and interpolate feels like it does two things. Generally it's good if functionality can be explained as doing one thing. Extraction seems to me to be something we do in service of the more important interpolation. The name also doesn't communicate that the method is primarily a tool for temperature interpolation at layer boundaries. This makes the tool seem like it's generic when it surely is not.

How about BoundaryTemperatureInterpolation?

Or LayerTemperatureInterpolation or TemperatureInterpolationAtLayers?

I think you are correct, the main overarching thing the function does here is Interpolate temperature at given heights. The extraction depends upon the boundary arguments that we provide. So it make sense to rename the plugin to LayerTemperatureInterpolation

robertplatt-mo · 2026-03-06T13:27:00Z

improver/temperature/layer_mean_temperature.py

+        Extract and interpolate temperature values at layer boundaries.
+
+        Args:
+            temp_cube (iris.cube.Cube): Input temperature cube with a height coordinate.


Ryan has previously informed me that the way improver docs are generated we don't need type hints in the args as these can be dynamically generated for the types (for more info on this though probably best to ask him).

I noticed this and then subsequently noticed we haven't got any type hints. My understanding is the improver style guide has these as a requirement. Please consider this comment to apply to all docstrings and all methods (sorry I know it's a pain).

robertplatt-mo · 2026-03-06T13:28:05Z

improver/temperature/layer_mean_temperature.py

+            iris.Constraint(
+                height=lambda point: bottom / self.metres_to_ft
+                < point
+                < top / self.metres_to_ft


As noted above I don't think we should be passing this in (but please correct me if I'm mistaken and there is a good reason I am not aware of). I'd set it at the top of the file as a constant.

robertplatt-mo · 2026-03-06T13:30:29Z

improver/temperature/layer_mean_temperature.py

+        if verbosity:
+            print("Layer mean temperature array:", lmt_array)
+
+        # Wrap result in a cube (add metadata as needed)


Suggested change

# Wrap result in a cube (add metadata as needed)

# Wrap result in a cube and add required metadata

As needed rather implies the user will choose what metadata is added imv

Anzerkhan27 · 2026-03-09T10:33:46Z

@Anzerkhan27 I've requested a few changes the main comments being in layer_mean_temperature and probably the most time consuming being type hints which I understand improver style guide expects.

Generally it all looks pretty sensible though.

Thank you @robertplatt-mo . I have added the METRES_TO_FT as a constant at top of the file rather than as an argument, changed the plugin name to reflect its main function. I have also added type hints in the method signature and removed it from the docstrings. Also added the small changes to the comments and Docstrings

mo-DavidJohnJohnston · 2026-03-09T11:40:44Z

improver/temperature/layer_mean_temperature.py

+
+        Args:
+            layer_cube: Cube containing temperature at all heights within
+                the specified layer (including interpolated base and top).


indent here inconsistent

mo-DavidJohnJohnston · 2026-03-09T11:51:55Z

improver/temperature/layer_mean_temperature.py

+
+        # Add contributions from base and top
+        layer_temp_product += (
+            layer_cube.data[0, :, :] * (altitude_array[1] - altitude_array[0]) / 2


not sure this factor of 2 should be present (and as below) - as we are looking at adjacent layers in the calculations. In the calculation above we are looking at layers which are 2 gaps apart.

I did some checks and the calculation looks more or less right. It's rather unconventional as a double sized-gap is used for most of the calculation, buy everything is divided by 2, even the single-size gaps at the top and bottom, but the terms balance out.

mo-DavidJohnJohnston · 2026-03-09T13:49:18Z

improver_tests/temperature/layer_mean_temperature/test_calculate_layer_mean_temperature.py

+    """
+    height_points = np.array([100, 200, 300], dtype=np.float32)
+    y_points = np.array([0, 1], dtype=np.float32)
+    x_points = np.array([0, 1], dtype=np.float32)


If lines 22-24 were customised to the shape of the input data, then
make_layer_cube would be more general. I think make_layer_cube
could be used in more places in the unit tests.

mo-DavidJohnJohnston · 2026-03-09T13:50:00Z

improver_tests/temperature/layer_mean_temperature/test_layer_temperature_interpolation.py

+    # Should include interpolated base (600ft), all interior levels, and interpolated top (800ft)
+    # In this synthetic example, all heights are present, so result should have 5 heights
+    assert result.shape == (5, 2, 2)
+    # Check height coordinate values


excellent commenting!

Add layer extraction and interpolation plugin

bb0a3e1

Anzerkhan27 changed the title ~~Add layer extraction and interpolation plugin~~ Add Improver plugins to calculate Layer Mean temperature for Triggered Lightning Mar 3, 2026

Anzerkhan27 added 6 commits March 4, 2026 12:27

Add calculate layer mean temperature plugin

c4579b6

Add doctsrtings

67925e4

Add unit tests for layer extraction and interpolation

38b9321

Add unit test for CalculateLayerMeanTemperature plugin

8b2d3ce

Add unit tests for edge cases

3d198f7

Merge remote-tracking branch 'origin/master' into EPPT-2747-triggered…

0ca3d0c

…-lightning-layer-mean-temperature-plugin

Anzerkhan27 changed the title ~~Add Improver plugins to calculate Layer Mean temperature for Triggered Lightning~~ Triggered Lightning: Implement Layer Mean Temperature Plugins Mar 5, 2026

refactor: Test file renamed

9725faf

robertplatt-mo requested changes Mar 6, 2026

View reviewed changes

refac: robert changes

0d1ca78

Anzerkhan27 requested a review from robertplatt-mo March 9, 2026 10:39

mo-DavidJohnJohnston reviewed Mar 9, 2026

View reviewed changes

	raise ValueError(f"bottom ({bottom} ft) must be less than top ({top} ft).")
	raise ValueError(f"Bottom ({bottom} ft) must be less than top ({top} ft).")

		from improver import BasePlugin


		class LayerExtractionAndInterpolation(BasePlugin):

	# Wrap result in a cube (add metadata as needed)
	# Wrap result in a cube and add required metadata

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Anzerkhan27 commented Mar 3, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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1. LayerExtractionAndInterpolation

2. CalculateLayerMeanTemperature

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Anzerkhan27 commented Mar 3, 2026 •

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1. `LayerExtractionAndInterpolation`

2. `CalculateLayerMeanTemperature`

Anzerkhan27 Mar 9, 2026 •

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robertplatt-mo Mar 6, 2026 •

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Anzerkhan27 commented Mar 9, 2026 •

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